1. Field of the Invention
The present invention generally relates to a method for forming a Group III-V semiconductor layer, in particular, to a nitride semiconductor layer and a forming method thereof.
2. Description of Related Art
Recently, light-emitting diodes (LED) and laser diodes (LD) have been widely applied to the market. For example, a white light can be obtained by combining a blue fluorescent powder with a yellow fluorescent powder manufactured by GaN, which is not only brighter and more power-saving than that of the conventional bulb, but also greatly reduces the power consumption. In addition, the service life of the LED is approximately over several ten thousand hours, which is much longer than that of the conventional bulb.
During the process of manufacturing the GaN semiconductor light emitting device, a GaN semiconductor layer and a heterogeneous substrate have difference lattice constants and thermal expansion coefficients, so the penetration dislocation and thermal stress problems easily occurs for the GaN semiconductor during the epitaxy process, so as to seriously affect a light emitting efficiency of the light emitting device. Then, the poor thermal conductivity of the heterogeneous substrate also be a main factor that would decay devices efficiency.
Conventionally, the process for separating the GaN semiconductor layer from the heterogeneous substrate includes a light irradiation manner, in which the laser light penetrates the substrate and irradiates an interface between the substrate and the GaN semiconductor layer, so as to separate the GaN semiconductor layer from the heterogeneous substrate. In addition, it is also possible to directly remove the barrier structure between the substrate and the GaN semiconductor layer through wet etching, so as to weaken the connection structure between the GaN semiconductor layer and the heterogeneous substrate, thereby separating the GaN semiconductor layer from the heterogeneous substrate. In addition, an interface layer between the GaN semiconductor layer and the heterogeneous substrate may be directly removed by performing a vapour phase etching (VPE) under high temperature, so as to separate the GaN semiconductor layer from the heterogeneous substrate.
However, all the above methods cannot modify the deterioration of the light emitting efficiency of the GaN semiconductor layer resulted from both the penetration dislocation and thermal stress during the epitaxy process at the same time.